1. Field of the Invention
The present invention relates to an overcharge protection device and method that include a diagnostic function.
2. Description of the Related Art
Generally, a lithium-ion battery, which is a rechargeable battery, may explode and ignite when it is overcharged. Also, a battery module usually includes multiple battery cells in order to provide the required output power. When any one of the battery cells included in the battery module is overcharged and thus explodes or ignites, it may affect not only the overcharged battery cell but also the other battery cells. Therefore, it is essential to prevent the battery from being overcharged in order to secure the safety of the battery.
Generally, overcharge protection devices may be categorized into electrical overcharge protection devices and mechanical overcharge protection devices.
An electrical overcharge protection device continuously monitors the voltage of a battery cell by being connected to one of the cells included in a battery module. When the battery cell is overcharged and the voltage of the battery cell exceeds a certain voltage, the electrical overcharge protection device opens the switch of a main relay by interrupting the supply of voltage applied to the actuation coil of the main relay, whereby the electrical connection between the battery module and the charging power source or load is disconnected.
The mechanical overcharge protection device continuously monitors whether a battery cell abnormally swells by being connected to one of the cells included in a battery module. When the battery cell is overcharged and the internal pressure thereof increases, the battery cell swells. In this case, the swelling of the battery cell causes the mechanical overcharge protection device to open the switch of a main relay by opening a closed circuit that includes the actuation coil of the main relay, whereby the electrical connection between the battery module and the charging power source or load is disconnected.
However, because a conventional mechanical overcharge protection device does not include a diagnostic function for the overcharge protection device itself, it may not determine whether the mechanical overcharge protection device is in a normal state or in a nonfunctioning Ss state, and may not check whether the overcharge protection operation, which actually disconnects the electrical connection between the battery module and the charging power source or load, has been performed appropriately in response to the abnormal swelling of the battery cell.
When the contact points of the mechanical overcharge protection device have worn down due to vibration or the like, the mechanical overcharge protection device may not operate normally due to failure of the contacts. Accordingly, even if the battery is overcharged and swells, the conventional mechanical overcharge protection device may not detect this, and the battery may explode or ignite.
A patent application mentioned below in the documents of the related art relates to a failure diagnosis circuit capable of diagnosing the failure of a switchgear unit installed in the charging and discharging path of a secondary battery while reducing the increase of discharge current of the secondary battery, and a battery pack including this failure diagnosis circuit. However, the patent application mentioned in the following documents of the related art may not diagnose the operating state and the failure of a mechanical overcharge protection device.
Therefore, required is an overcharge protection device and, method that can diagnose the operating state and the failure of a mechanical overcharge protection device.